Nov. i, 1920 Control of Fluke Diseases 205 



obviously vary greatly in different streams, according to evenness of 

 width and depth, strength of current, purity of water, and possibly 

 other factors, it would be necessary in treating any stream for the 

 destruction of snails to determine, after the experiment, the distance 

 over which it is effective and to repeat the experiment at a point on 

 the stream a little above where the first live snails were found. , 



By utilizing a 50-gallon barrel and filling it at 12-hour intervals with a 

 10 per cent solution, streams running as much as 3,500 gallons per 

 minute could be treated by this method, and, of course, by the use of 

 several such barrels, still larger streams could be treated. Repeated 

 attempts were made to find a method by which the copper salt could be 

 fed into a stream at a constant rate without first being put into solution. 

 This would, of course, save much time and labor in the treatment of 

 large streams. A method was finally worked out by which it was hoped 

 that this could be accomplished. Cylinders of sheet metal were care- 

 fully lined with paraffine inside to prevent any chemical action with the 

 copper sulphate. Wooden tubes could be used as well but are not so 

 readily obtainable as are the sheet metal tubes, which, in diameters of 

 from 2 inches up, can be obtained from any tinsmith. A copper or 

 bronze screen is tied over the end of the tube, and the tube is filled with 

 copper-sulphate crystals of more or less uniform size. Commercial 

 "pea" crystals could be used, or crystals of desired size can be obtained 

 by sifting through two screens. The screened end of the tube is immersed 

 about 1 cm. in the stream to be treated, and the copper sulphate is dis- 

 solved out from the bottom of the tube, a fresh supply being constantly 

 furnished by gravity in the tube. Theoretically the copper salt should 

 go into solution at a fairly constant rate, determined by the area exposed 

 to the water, the speed of the stream, and the temperature of the water. 

 Up to the present, however, it has not been found possible to make this 

 simple apparatus work satisfactorily in practice, because of the fact that 

 all the water in the vicinity of Houston is strongly alkaline. The alka- 

 linity precipitates the iron sulphate contained as an impurity in com- 

 mercial copper sulphate and also forms, in the course of two or three 

 hours, considerable deposits of copper carbonates. These two substances 

 together tend to clog the screen through which the copper sulphate is 

 taken into solution, thus causing a rapid diminution in the rate of solu- 

 tion. If this difficulty could be overcome by some feasible method of 

 keeping the water at the mouth of the tube slightly acidified, or if the 

 water to be treated were not alkaline, large streams could be treated 

 with comparatively little trouble by this method, using several tubes 

 of suitable diameter at intervals across the streams. It would, of course, 

 be preferable to treat streams at a comparatively shallow, rapid-flowing 

 point, since this would facilitate a rapid diffusion throughout the water. 



